1. Field of the Invention
The present invention relates to data communications, and more particularly to techniques for improving multicast distribution efficiencies in a dialup access environment.
2. Description of Related Art
Local loops connect modems at customers premises to a central office switch on the public switched telephone network. At the central office switch, the telephone connection is routed to its destination, either directly or through other equipment in the network. As data traffic increases, the companies that provide access to Internet Service Providers ISPs across their telephone networks (access providers) are diverting the data traffic off of the voice networks into networks more suited for data traffic or packet switched traffic. Thus, the central office switches are configured with a concentrator and multiplexer for data traffic which is split off of the voice traffic. The communication of the data traffic from the central office switch to a remote access server or other destination is processed by the concentrator/multiplexer to optimize use of the access provider's available bandwidth. For example, access providers are beginning to deploy equipment that diverts calls destined for Internet Service Providers off of the voice switching network, which terminates calls, extracts PPP packets and encapsulates the packets within logical connections in a tunnel. A tunnel is a communication channel which operates according to a tunneling protocol, including the point-to-point tunneling protocol PPTP, the layer 2 forwarding protocol L2F, the layer 2 tunneling protocol L2TP and equivalent protocols. The logical connections within a tunnel are used as a means for multiplexing the data from several users into a single tunnel.
Multicast applications are becoming increasingly popular over the Internet. These applications make use of the following interactions between Customer Premises Equipment (CPE) and an ISP's Remote Access Server (RAS):
Each endpoint that wishes to listen to a multicast feed joins the appropriate group by issuing an IGMP Join message towards the ISP RAS. The group will have a particular IP multicast address associated with it. The IGMP Join message is targeted to this multicast address. PA1 The ISP RAS will process all messages addressed to multicast group addresses. It will process the IGMP Join message, and become aware that the CPE wishes to receive the multicast feed. It will then replicate the multicast feed, and send it over a PPP session between itself and the CFE.
With multiple CPE issuing Joins, each CPE will receive its individual stream over its PPP session with the RAS. Thus, the RAS will replicate the data it receives for a multicast, and send it as individual streams over PPP sessions to individual CPE. This means that Wide Area Network (WAN) resources of the carrier have to be deployed to handle these replicated streams. With the advent of high bandwidth access such as Asymmetric Digital Subscriber Loop (ADSL) technology, each subscriber could receive several Mb/sec of traffic via a multicast feed. Replicating this places an onerous load on carrier networks, and requires expensive deployment of equipment to provide the needed capacity.